Characterization of a 23-mm Torch for Use in Inductively Coupled Plasma Mass Spectrometry

Abstract

A 23-mm-i.d. torch is described and evaluated for use in inductively coupled plasma mass spectrometry. The plasma operates optimally at 1.50 kW forward power and 19.2 L/min total argon flow. The effect of the customary operating parameters (nebulizer flow rate, rf power, sampling depth, and ion-lens voltages) on analyte signals is discussed. Detection limits, oxide-ion ratios, and doubly charged ion ratios have been measured and are compared with those produced by an 18-mm-i.d. low-flow MAK torch. When compared to the conventional torch, the 23-mm system exhibits comparable detection limits for low-mass ions but better detection limits for high-mass ions (Pb and U). Oxide-ion ratios are lower in the larger torch, but doubly charged ion ratios are higher. Because optimal sampling depths in the larger torch are higher, entrained air in the tail flame causes instability and results in increased ArO+ and ArN+ background signals.

Characterization of a 22 mm Torch for ICP-AES

“…In earlier studies, a larger torch was developed in hopes that it would better isolate the sample channel, and hence the analyte, from atmospheric gases. 8 This isolation m ight, in turn, reduce the fraction of polyatomic species in the plasma and therefore give less severe spectral or isobaric overlap. However, even after optimization of the system, 8 no reduction of oxide levels was reported.…”

“…8 This isolation m ight, in turn, reduce the fraction of polyatomic species in the plasma and therefore give less severe spectral or isobaric overlap. However, even after optimization of the system, 8 no reduction of oxide levels was reported. In fact, higher oxide/ion ratios were observed in the larger torch than in the conventional 18 m m torch.…”

“…Yet, at higher rf power levels, the stability of the plasma was sacri® ced. Norman et al 8 proposed that if the rf power could be increased, ions would be form ed lower in the plasma, so the sampling depth could be reduced and stability increased.…”